Some Menards home improvement centers sell propane like gas stations. Just let the service desk know you have your motor home parked in the filling area, ready for filling. Someone comes out and fills it for you. Their prices are generally very cheap. About one out of every three Menards in my area sells propane that way.
As others have mentioned, truck stops generally have propane filling stations of which I go to for the convenience when on a trip. But if needed when at home, it's off to Menards.